Beyonce and JAY-Z have offered fans who adopt at least a partially vegan diet the chance to win gig tickets for life.

The pop power couple previously urged people to give up meat by penning the introduction to her personal trainer, Marco Borges’ book The Greenprint: Plant-Based Diet, Best Body, Better World.

On Wednesday they announced the Greenprint Project, a contest allowing their U.S. admirers to win a ticket to a date on each of their tours for the next 30 years.

A post on Beyonce’s Instagram page urging fans to click on a link to the project’s website and enter the competition. They can do so by pledging to give up meat on at least one day a week, for certain meals or to go further by going fully vegan.

The stars first adopted a vegan diet by taking part in a month-long challenge in 2013, shortly after the birth of their first child Blue Ivy, and have stepped up their commitment to veganism since the birth of their twins Sir and Rumi.

In Marco’s book, they wrote about how having kids inspired them to live more healthily, for their own sake and that of the planet.

“Having children has changed our lives more than anything else,” they wrote. “We used to think of health as a diet – some worked for us, some didn’t. Once we looked at health as the truth, instead of a diet, it became a mission for us to share that truth and lifestyle with as many people as possible.”

In addition to offering fans the chance to enter the competition, the Greenprint Project website details the positive impacts of people cutting their meat consumption – listing the socially useful projects that could be powered by the emissions saved by humans consuming fewer animals.

Beyonce, 37, and Jay, 49, completed their joint On the Run II Tour in October.